The other day I read a post where Mesa Maltworks mentioned "scrubbing" in a keg. I would be interested in the procedure. From what I understand it helps purge volatiles from the beer. How does it do that? How do I get it to do that? What exactly are volatiles? IS that another word for off flavors? Are they an off flavor?

Volatiles are aromatic compounds that can affect flavors in beer. They are referred to as volatile because they can be driven off to varying degrees.

CO2 scrubbing is a process that is used primarily with lagers to remove sulfur flavors and aromas that are yeast produced so as to reduce conditioning time. This process can be used with any style to remove unwanted aromatics such as DMS and diacetyl as well as sulfur. You have to be cautious though... CO2 scrubbing will also reduce hop aromas as well. To counter this, dry hop after scrubbing.

How: Put the finished beer in a Cornelius cylinder and allow some extra air space for foaming. Leave the top cocked open and send CO2 through the LIQUID fitting. MAKE SURE YOU HAVE A CO2 CHECK VALVE INSTALLED OR YOU COULD SIPHON THE BEER INTO THE LINE !

Keep underletting the CO2 into the beer until you don't smell the compound you are trying to eliminate. Re-seal and condition as usual.

As far as flavor effects... sulfurs are aromatics and once gone, stay gone (in terminal beer). Diacetyl, however is both a flavor and an aromatic, so you can only drive it off somewhat.

As far as "off" flavors, one of the defining characteristics of most lagers is a slight sulfur flavor and sometimes aroma, but too much is unpleasant. This is why the technique evolved. I consider DMS always an "off" flavor except where it is intentional (ie...Rolling Rock) and the same goes for acetaldehyde (exception = Budweiser). As far as I know, acetaldehyde cannot be effected with this technique and luckily, I've never had to try it for this compound.